System and method for percutaneous myocardial revascularization

ABSTRACT

A method and apparatus are described for percutaneous myocardial revascularization of a human heart. A deflectable elongated flexible lasing apparatus is used which includes a source of laser radiation, an elongated flexible radiation conveying means for conducting the laser radiation to a lens on the distal end of the radiation conveying means for focusing the laser radiation, and control lines for deflecting the distal end of the radiation conveying means. The control lines are secured to the distal end of the radiation conveying means for changing the angle of deflection of the distal end of the radiation conveying means. The lasing apparatus is guided to an area within the patient&#39;s heart, and the distal end of the lasing apparatus is directed to an area of interest where the inner wall of the heart is irradiated with laser energy to form a channel through the myocardium for a desired distance. In a preferred embodiment, channels are formed without perforating the epicardium of the heart.

This is a continuation of application Ser. No. 07/630,258, filed Dec.18, 1990, now abandoned.

FIELD OF THE INVENTION

This invention is generally directed to the field of laser surgery, andmore particularly to laser surgery procedures to improve the flow ofblood to the heart muscle.

BACKGROUND OF THE INVENTION

The number and variety of medical methods available to repair theeffects of cardiovascular disease has increased rapidly over the lastseveral years. More particularly, alternatives to open heart surgery andcardiovascular by-pass surgery have been extensively investigated,resulting in non-surgical procedures such as percutaneous transluminalcoronary angioplasty, laser angioplasty, and atherectomy. Theseprocedures are primarily directed toward the reduction of stenosiswithin the vasculature of a patient by either expanding the lumenthrough the use of a balloon, or ablating or otherwise removing thematerial making up the stenosis.

While these procedures have shown considerable promise, many patientsstill require bypass surgery due to such conditions as the presence ofextremely diffuse stenotic lesions, the presence of total occlusions andthe presence of stenotic lesions in extremely tortuous vessels. Also,some patients are too sick to successfully undergo bypass surgery, andbecause the above treatments require surgical backup in the case ofcomplications, they are untreatable. Some patients requiring repeatbypass surgeries are also untreatable.

One alternative to these procedures is known as Laser MyocardialRevascularization (LMR). In LMR, channels are formed in the heart wallwith a laser. These channels provide blood flow to ischemic heartmuscle. A history and description of this method is presented by Dr. M.Mirhoseini and M. Cayton in "Lasers in Cardiothoracic Surgery" in Lasersin General Surgery (Williams & Wilkins; 1989) pp. 216-223.

In the procedure described therein, a CO₂ laser is used to producechannels in the heart wall from the epicardium through the endocardium.This procedure follows a surgical cutdown. External pressure is used tostop bleeding from the interior of the heart to the outside. Dr.Mirhoseini has documented that although the channel is sealed at theepicardial layer, it remains patent in the endocardial and myocardiallayers. Laser energy is transmitted from the laser to the epicardium bymeans of an articulated arm device that is commonly used for CO₂ lasersurgery.

A proposed improvement in the design is described in Hardy--U.S. Pat.No. 4,658,817. A needle is added to the distal tip of the articulatedarm system, with laser energy passing through the lumen of the needle.The metal tip of the needle of the device is used to pierce most of themyocardium and the laser beam is used to create the desired channelthrough the remaining portion of the myocardium and through the adjacentendocardium.

Hardy contends that mechanical piercing serves to facilitate sealing ofthe epicardial portion of the channel. Mechanical piercing is highlyundesirable, because such piercing always entails some degree of tearingof the pierced tissue. Tearing leads to fibrosis as the mechanical tearheals. Fibrosis severely diminishes the effectiveness of the LMRtreatment.

These LMR procedures still require that the chest wall be opened inorder to access the heart muscle with presently utilized laser devices.Thus these procedures require major surgery which is highly invasive andwhich may result in severe complications.

An additional problem associated with those procedures utilizing anarticulated arm device is that the articulated arm is difficult tomanipulate. Thus portions of the heart may be effectively unreachable bythe device.

Broadly, it is the object of the present invention to provide animproved apparatus and method for performing laser myocardialrevascularization.

It is a further object of the present invention to provide an apparatusand method for performing laser myocardial revascularization which canbe performed percutaneously.

It is a still further object of the present invention to provide anapparatus and method for performing laser myocardial revascularizationwhich can access difficult to reach portions of the heart.

It is a yet further object of the present invention to provide anapparatus and method for performing laser myocardial revascularizationwhich allow for monitoring of the creation of the percutaneously createdchannels.

These and other objects of the present invention will be apparent tothose skilled in the art from the following detailed description and theaccompanying drawings.

SUMMARY OF THE INVENTION

The apparatus of the present invention comprises an elongated flexiblelasing apparatus. The apparatus includes a source of laser radiation.The apparatus also includes an elongated flexible radiation conveyingmeans having proximal and distal ends. In the preferred embodiment ofthe invention, the radiation conveying means comprises an optical fiber.The radiation conveying means is operatively connected to the source oflaser radiation to receive the laser radiation and conduct the laserradiation to be emitted at the distal end. The lasing apparatus alsoincludes lens means at the distal end of the radiation conveying meansfor controlling the laser radiation emitted from the distal end of theradiation conveying means. The lasing apparatus further includes meansfor guiding the distal end of the radiation conveying means through thevasculature of a patient and positioning that distal end so as to directthe laser radiation upon a fixed portion of tissue. In the preferredembodiment, the lasing apparatus is disposed within a steerable ordeflectable guiding catheter.

In a preferred embodiment of the present invention, the means forguiding the distal end of the radiation conveying means comprises aplurality of control lines having proximal and distal ends. Those distalends are secured at the distal end of an optical fiber laser apparatus.The guiding means further includes means at the proximal ends of thecontrol lines for axially moving the control lines. The axial movementchanges the angle of the distal end of the optical fiber with respect tothe proximal end of the optical fiber.

The method of the present invention comprises a method of percutaneousmyocardial revascularization of the myocardium of the heart of apatient. The method includes the step of inserting a guidable elongatedflexible lasing apparatus into a patient's vasculature. The distal endof the lasing apparatus is guided to an area in the heart to berevascularized. Then the inner wall of the heart is irradiated withlaser energy emitted from the distal end of the lasing apparatus. Thisirradiation is performed with sufficient energy and for a sufficienttime to cause a channel to be formed from the endocardium into themyocardium for a desired distance.

In alternative embodiments of the present invention, the elongatedflexible radiation conveying lasing means comprises an optical waveguidesuitable for use with a CO₂ or other laser.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic section of a human heart showing revascularizationof the myocardium according to the invention.

FIG. 2 is a schematic cross-section of a deflectable lasing apparatusembodying the features of the invention.

FIG. 3 is a cross-section of a preferred lens design for the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As is shown in the drawings, which are provided for purposes ofillustration and not by way of limitation, the apparatus of the presentinvention is embodied in a system for revascularization of themyocardium of a human heart 10. As is illustrated in FIG. 1, thedeflectable elongated flexible lasing apparatus 12 is inserted into thevasculature of a patient, generally through one of the major vessels 14,thereby affording access for the apparatus to an area such as aventricle 16 having an area 18 in need of increased blood circulationdue to cardiovascular disease. Portions of the heart other than theventricles might also be revascularized by this method. A number ofchannels 20 can be formed by lasing apparatus 12 from the inner wall, orendocardium 22, and extend a desired distance through the myocardium 24without perforating the exterior of the heart wall, the epicardium 26.

Lasing apparatus 12 includes a remotely located source of laser energy30 connected to the proximal end 34 of an elongated flexible radiationconveying means, which in the preferred embodiment comprises an opticalfiber 32. Laser 30 may typically be an HO YAG laser, for example,although other sources of energy, such as excimer lasers, are adaptableto the invention. Optical fiber 32 conducts the laser energy to itsdistal end 36. Optical fiber 32 may, in a preferred embodiment, beapproximately 240 microns in diameter. This diameter optical fiber hasthe required flexibility for passage through the vasculature, and yetmay be reinforced in a variety of ways to prevent breakage.

It will be apparent to those skilled in the art that a CO₂ laser may beused as laser 30 if a suitable optical fiber or waveguide is used as itsradiation conveying means. While the discussion hereafter refers tooptical fiber devices, the present invention is not limited to thatparticular implementation of a radiation conveying means.

Referring to FIG. 2, a lens 38 having a sleeve 40, is preferablyconnected to the distal end 36 of optical fiber 32. Although lens 38 isillustrated in FIG. 2 as being a ball type lens, the preferredembodiment of lens 38 is illustrated in FIG. 3, which is discussedbelow. Lens 38 focuses and concentrates the laser energy emitted byoptical fiber 32.

Optical fiber 32 may be housed in a catheter which may incorporate oneor more other functions in addition to the housing of optical fiber 32.The catheter may, for example, also provide for a guidewire over whichthe catheter may be advanced. The present invention is also adaptable toa guiding catheter used to initially position the catheter which housesoptical fiber 32.

In one preferred embodiment of the present invention, a plurality ofcontrol lines 42 are connected at their distal ends to the distal end 36of optical fiber 32, such as by adhesive bonding 44. Adhesive bonding 44may utilize any of a variety of adhesives. At least two, and preferablyfour, control lines 42 are thus axially, and preferably symmetrically,disposed on optical fiber 32. Axial movement of control lines 42 willthus change the angle of deflection of distal end 36 of optical fiber 32with respect to its proximal end 34. Means (not shown) such as a ring orknob may be attached to the proximal ends of control lines 42 to allowmanipulation of control lines 42. Control lines 42 are preferablyapproximately 3-mil stainless steel wire, but may be similar diameterfilaments, such as nylon, or other suitable materials.

In addition, an outer tubular member 46 preferably encloses controllines 42 and optical fiber 32, forming a protective covering. Outertubular member 46 is secured at its distal end to distal end 36 ofoptical fiber 32, rearward of lens 38. In order to facilitate precisecontrol of the tip during the procedure, control lines 42 are routedthrough spaced apart channels 48 that are attached to the outer surfaceof optical fiber 32. Channels 48 are preferably constructed of 30 gaugepolyamide tubing. Control lines 42 are thus guided to remain bothseparated and within well controlled areas on the exterior of opticalfiber 32, thus allowing for the accurate guidance of the catheterthrough the remote manipulation of control lines 42.

Referring to FIG. 3, it has been found that in a preferred embodiment ofthe invention, a lens 350 is configured to include an essentiallycylindrical outer surface 352 terminating in a convex distal tip 354. Anoptical fiber 332 extends into an internal cavity 356 and terminates ina position spaced apart from an internal aspheric or ogival shapedsurface 358, the cavity apex 360 of which is distal from distal end 336of fiber 332. The interface 362 between optical fiber 332 and lens 350is reinforced, preferably with epoxy 364 or the like, although othermeans of reinforcement designed to prevent dislodging of the lens areadaptable to the invention.

Optical fiber 332 may also be provided with one or more photo-opaquegold bands 366 located so as to provide an indication of the location ofthe probe on a fluoroscope or the like. Optical fiber 332 may be securedin the cavity by an adhesive 370, such as epoxy or the like, and thepolyamide coating 372 of optical fiber 332 may be removed at the distalend to improve the optical qualities of the lens.

The basic method of the present invention has been laid out above.Lasing apparatus 12 is inserted into the vasculature of a patient,generally through one of the major vessels 14, thereby affording accessfor the apparatus to an area such as a ventricle 16 having an area 18 inneed of increased blood circulation due to cardiovascular disease. Anumber of channels 20 can be formed by lasing apparatus 12 from theinner wall, or endocardium 22, and extend a desired distance through themyocardium 24 without perforating the exterior of the heart wall, theepicardium 26.

In operation, the distal end of lasing apparatus 12 may be maintained inposition on the inner heart wall 22 by a gentle pressure, to insure thatlasing apparatus 12 is not dislodged in the formation of the channelbetween pulses of the laser. Such pressure can be applied either bypushing the catheter forward into the tissue or by applying a vacuum atthe distal tip 36 of lasing apparatus 12. The heart beat is preferablymonitored, and the laser is preferably gated to generate one or morepulses during contractions (systole) of the heart, and to generate nopulses during the rest of the heart cycle. These procedures combine toanchor lasing apparatus 12 to a relatively stable location on the tissuethat is to be ablated.

It has been found that the heart muscle is much more dense near theexterior surface and thus the cutting occurs fairly rapidly for a givenlaser energy output in the myocardium and diminishes as the exteriorportion of the heart known as the epicardium is approached. Thus, theperson conducting the procedure can accurately determine the amount ofrevascularization by the speed with which the catheter progresses. Theprobe cuts while in contact, so tactile sense is preserved. This permitstermination of the cutting of a given channel prior to the piercing ofthe exterior of the heart muscle.

Another method of guiding the lasing apparatus into a proper positionwithin the heart is to place the lasing apparatus 12 within adeflectable guiding catheter (not shown) having x-y steerability, for anadded degree of steerability and control of the lasing apparatus. Inpractice, the positioning of the device may be viewed by esophagealultrasound imaging or fluoroscope imaging. It may also be desirable toadd one or more radiopaque marker bands to the distal portion 36 oflasing apparatus 12, for fluoroscopic imaging. Lasing apparatus 12 maythereby be aimed and controlled for forming channels 20 in themyocardium of the heart for revascularization of areas of the heart inneed of improved blood flow.

In early experiments with an HO laser, it was found that it may bedesirable to begin the procedure with approximately 0.65 j pulses, at afrequency of at least 2 Hz, in order to penetrate the endocardium, andthen decrease the laser power to approximately 0.2 j to form the channelin the myocardium. This minimizes the need for anchoring the catheter tothe area to be treated. Note that the dosimetry is dependent upon thediameter of the lens used.

In practice, it has been found that lens 350 of the embodiment of FIG.3, when in contact with tissue, cuts a lumen equal or greater than thelens diameter which is in front of and axially aligned with the axis ofthe lens. This provides improved ablation into the heart muscle ofchannels of the type preferred in this method. As the channel is cut,the cylindrical outer surface 352 assists in guiding and controlling thecatheter during the cutting process. The angle of the projected energyfrom the lens can also be controlled by some degree with the separationof distal tip 336 of optical fiber 332 from the cavity distal apex 360.It has also been found that the construction is scalable.

It has been found that channels that are approximately 1.5 mm-2.0 mm indiameter and approximately 1 to 3 cm deep may easily and efficiently becut by this method, and that the revascularization proceduredramatically improves the flow of blood to the heart muscle, therebydecreasing the probability of heart attack from occlusion of theexternal vasculature of the heart.

The method of the present invention overcomes the difficulty ofachieving the fine precision required in laser angioplasty and is usefulfor patients with advanced disease or with vasculature who might nototherwise be candidates for angioplasty procedures. It is evident thatthe method and apparatus for myocardial revascularization overcomesproblems of spasm and occlusion of blood vessels supplying the heart,and that myocardial revascularization offers a valuable alternative formof treatment of heart disease which may be used separately or inconjunction with other treatments. In addition, the present inventionmay be suitable for those too sick for bypass surgery, as well as forthose patients with myocardium at risk.

There has been described herein an elongated flexible lasing apparatusand method for percutaneous myocardial revascularization. Variousmodifications to the present invention will become apparent to thoseskilled in the art from the foregoing description and accompanyingdrawings. Accordingly, the present invention is to be limited solely bythe scope of the following claims.

What is claimed is:
 1. A method of percutaneous myocardialrevascularization of the myocardium of the heart of a patient,comprising the steps of:inserting a guidable elongated flexible lasingapparatus into a patient's vasculature; guiding the distal end of saidlasing apparatus to an area within the patient's heart; directing saiddistal end of said lasing apparatus to an area within the heart to berevascularized; and irradiating the inner wall of the heart with laserenergy emitted from said distal end of said lasing apparatus withsufficient energy and for a sufficient time to cause a channel to beformed extending from the inner surface of the myocardium.
 2. The methodof claim 1 further including the steps of monitoring the systole anddiastole of the heart cycle, and performing said step of irradiating theinner wall of the heart with laser energy in a plurality of pulsesduring systole of the heart cycle.
 3. The method of claim 1, furtherincluding guiding said lasing apparatus through a deflectable guidingcatheter.
 4. The method of claim 1, wherein said channel is formedcompletely through the endocardium and partially through the myocardiumof the heart.
 5. The method of claim 1, wherein said step of guidingsaid distal end of said lasing apparatus to an area within the patient'sheart further comprises the steps of inserting a guidewire into thatarea and passing a catheter through which said lasing apparatus extendsover said guidewire.
 6. A method of improving the circulation of bloodto the muscle of the heart of a patient, comprising the stepsof:directing a means for forming a channel in the heart muscle into thepatient's vasculature; guiding the distal end of said channel formingmeans to an area of interest within the patient's heart to whichincreased blood flow is desired; and controlling said channel formingmeans to create channels in the heart muscle in the area of interest. 7.The method of claim 6, wherein said channels are formed withoutperforating the exterior of the heart wall.
 8. The method of claim 6,wherein said channel forming means comprises an lasing apparatus, andsaid step of controlling said channel forming means comprises directinga laser energy emission in a concentrated beam from said lasingapparatus on the inner wall of the heart in the area of interest.
 9. Themethod of claim 6, further including the steps of monitoring the systoleand diastole of the heart cycle, and performing said step of directingsaid laser energy emission on the inner wall of the heart in a pluralityof pulses during systole of the heart cycle.
 10. The method of claim 6,further including guiding said channel forming means through adeflectable guiding catheter.
 11. The method of claim 6, furtherincluding placing a guidewire into the patient's vasculature and guidingsaid channel forming means over said guidewire.